On Tue, 30 Mar 2010 12:25:15 +0100, The Natural Philosopher wrote:

Chlorine gas is given off as it reacts with the limescale.

It shouldn't be.

I'd be surprised but you can get chlorine out of loo if you pee into
bleach IIRC. I wouldn't like to say what is also locked up in the
"lime scale" of a toilet pan.

I think I'd give the supermarket toilet lime scale removers a chance
first before bring out the heavy guns of brick acid.

--
Cheers
Dave.